Eukaryotic Viruses

Taxonomy characters:

• nucleic acid type;

• enveloped or naked;

• capsid shape;

• assembly site in host (nucleus or cytoplasm)

Attachment and Penetration:Attachment phase is conceptually similar to phage.

Penetration can be very different (capsid may enter).

Enveloped virus fusing with endosome membrane for release of capsid.

NOTE: in both mechanisms the nucleic acid is “uncoated”, i.e. capsid disassembles.

DNA virus Papovavirus

(warts)

Transcription & replication in nucleus; capsid assembly in nucleus.

Release by

exocytosis

RNA Virus TypesPolio; common cold

(RdRp)

In the cytoplasm.

In the cytoplasm; except influenza

Orthomyxoviruses (Influenza Virus):

• Attachment and penetration by endocytosis, then -ssRNA is uncoated.

• Unique for RNA viruses to replicate in the nucleus; Uses RdRp to make +ssRNA then to –ssRNA.

• Needs a capped primer (C) for mRNA synthesis and ribosome recognition; steals C from host mRNA at 5’end.

• Viral envelope proteins transported from RER to GA to plasma membrane; others associate with –ssRNA to form nucleocapsid. Budding release (below):

RNA viruses= respiratory enteric orphan viruses

In the cytoplasm.

In the cytoplasm.

Retrovirus (+RNA)

Infection Types and Outcomes• Acute versus Persistent Infections:

– Chronic (replicates at low levels & constant yet mild symptoms)– Latent (stops reproduction after initial infection; goes dormant until

induced to activate replication again)– Slow (vary slow replication and spread; years before symptoms)

• Cytocidal effects (death) and cell damage:– Inhibit host macromolecule synthesis– Lysosome malfunction (host cell self digests)– Plasma membrane abnormalities– Direct viral protein toxicity– Protein aggregation (inclusion bodies)– Host cell changes to a malignant cell (cancer)

• Tumors form by neoplasia and anaplasa; may spread by metastasis.• Virus may carry oncogenes (genes for various cancer causing protein).• Viral promotors may insert and turn on expression of host oncogenes.• 8 cancers involving viruses: Burkitt’s lymphoma and nasopharyngeal

carcinoma (Epstein-Barr virus); cervical cancer (papillomavirus); Kaposi’s sarcoma (herpes 8), Hepatitis B & C, T-cell and hairy-cell leukemias, Rous sarcoma.